This type of the connection assemble is disclosed by Laid-open Japanese Patent Application No. 7-119884 by way of illustration in which a duct assemble introduces domestic waste water to run into a main ribbed duct. The main duct has an array of ribs around its securement opening. A branch duct has a saddle flange which has undulating wavy portions. Upon putting the branch duct on the main duct for connection, the undulating wavy portions interfit into the ribs of the main duct. At this time, an adhesive agent may be applied to the connection portion between the saddle flange and the main duct. The saddle flange may be tightly bound to the main duct by means of a wire band. Otherwise, the saddle flange is tightly secured to the main duct by engaging a pawl against an inner wall of the main duct.
However, both the main duct and the saddle flange are formed by a hard synthetic resin material, and the saddle flange may slide against the main duct if they are shaken when subjected to an exterior force. In addition, the adhesive agent may deteriorate to fall off the saddle flange. This would result in the water leakage at the connection between the saddle flange and the main duct. This is all the more prone to the water leakage because the adhesive agent is not per se suited to a water sealing action.
Therefore, the present invention has been made with the above drawbacks in mind, it is an object of the invention to provide a duct connection assemble which is capable of positively sealing a connection between a main duct and a saddle flange to prevent a water leakage for an extended period of time with a relatively simple structure.